<template>
    <div>
        <input ref="excel-upload-input" class="excel-upload-input" type="file" accept=".xlsx, .xls" @change="handleClick">
        <div class="drop" @drop="handleDrop" @dragover="handleDragover" @dragenter="handleDragover">
            Drop excel file here or
            <el-button :loading="loading" style="margin-left:16px;" size="mini" type="primary" @click="handleUpload">
                Browse
            </el-button>
        </div>
    </div>
</template>

<script>
import XLSX from "xlsx";

export default {
    props: {
    beforeUpload: Function, // eslint-disable-line
    onSuccess: Function// eslint-disable-line
    },
    data() {
        return {
            loading: false,
            excelData: {
                header: null,
                results: null
            }
        };
    },
    methods: {
        generateData({ header, results }) {
            this.excelData.header = header;
            this.excelData.results = results;
            this.onSuccess && this.onSuccess(this.excelData);
        },
        handleDrop(e) {
            e.stopPropagation();
            e.preventDefault();
            if (this.loading) return;
            const files = e.dataTransfer.files;
            if (files.length !== 1) {
                this.$message.error("Only support uploading one file!");
                return;
            }
            const rawFile = files[0]; // only use files[0]

            if (!this.isExcel(rawFile)) {
                this.$message.error("Only supports upload .xlsx, .xls, .csv suffix files");
                return false;
            }
            this.upload(rawFile);
            e.stopPropagation();
            e.preventDefault();
        },
        handleDragover(e) {
            e.stopPropagation();
            e.preventDefault();
            e.dataTransfer.dropEffect = "copy";
        },
        handleUpload() {
            this.$refs["excel-upload-input"].click();
        },
        handleClick(e) {
            const files = e.target.files;
            const rawFile = files[0]; // only use files[0]
            if (!rawFile) return;
            this.upload(rawFile);
        },
        upload(rawFile) {
            this.$refs["excel-upload-input"].value = null; // fix can't select the same excel

            if (!this.beforeUpload) {
                this.readerData(rawFile);
                return;
            }
            const before = this.beforeUpload(rawFile);
            if (before) {
                this.readerData(rawFile);
            }
        },
        readerData(rawFile) {
            this.loading = true;
            return new Promise((resolve, reject) => {
                const reader = new FileReader();
                reader.onload = e => {
                    const data = e.target.result;
                    const workbook = XLSX.read(data, { type: "array" });
                    const firstSheetName = workbook.SheetNames[0];
                    const worksheet = workbook.Sheets[firstSheetName];
                    const header = this.getHeaderRow(worksheet);
                    const results = XLSX.utils.sheet_to_json(worksheet);
                    this.generateData({ header, results });
                    this.loading = false;
                    resolve();
                };
                reader.readAsArrayBuffer(rawFile);
            });
        },
        getHeaderRow(sheet) {
            const headers = [];
            const range = XLSX.utils.decode_range(sheet["!ref"]);
            let C;
            const R = range.s.r;
            /* start in the first row */
            for (C = range.s.c; C <= range.e.c; ++C) { /* walk every column in the range */
                const cell = sheet[XLSX.utils.encode_cell({ c: C, r: R })];
                /* find the cell in the first row */
                let hdr = "UNKNOWN " + C; // <-- replace with your desired default
                if (cell && cell.t) hdr = XLSX.utils.format_cell(cell);
                headers.push(hdr);
            }
            return headers;
        },
        isExcel(file) {
            return /\.(xlsx|xls|csv)$/.test(file.name);
        }
    }
};
</script>

<style scoped>
.excel-upload-input{
  display: none;
  z-index: -9999;
}
.drop{
  border: 2px dashed #bbb;
  width: 600px;
  height: 160px;
  line-height: 160px;
  margin: 0 auto;
  font-size: 24px;
  border-radius: 5px;
  text-align: center;
  color: #bbb;
  position: relative;
}
</style>
